1. Field of the Invention
The present invention relates to a motor-driven power steering apparatus.
2. Description of the Related Art
A motor-driven power steering apparatus detects a steering torque of a steering system by a steering torque sensor. The apparatus sets a target current on the basis of the detected steering torque, drive controls an electric motor on the basis of a pulse width modulation (PWM) signal obtained by applying a proportional integral (PI) compensation to a deviation between a target current and a current actually flowing through the electric motor so as to linearly stroke a rack shaft, and applies a steering assist force to a wheel coupled to the rack shaft. This type of apparatus is described in Japanese Patent Application Laid-open No. 6-8839 (patent document 1).
When a vehicle is in a traveling state, the vehicle has the tendency of restoring a steering angle to a neutral position on the basis of a straight travel restoring function of the vehicle. However, in a vehicle stop state in which the straight travel restoring function is not executed, if a driver pauses manual steering by detaching a hand from the steering wheel or the like, the steering angle stops at a steering angle position where the driver made the pause of the manual steering without returning to the neutral position.
Accordingly, in the case of making a stop while turning the steering wheel by manual steering for parallel parking or the like, the steering wheel starts moving from the turned steering angle when next starting the vehicle. Accordingly, there is a risk that the vehicle is brought into contact with a peripheral obstacle. In order to prevent the contact, it is necessary to check out the turning angle (the steering angle position) of the wheel before the driver gets in the vehicle.